The invention is directed to a grooved horn radiator with a mode coupler for obtaining the ground wave and at least one higher wave type for self-follow up of an antenna on a moving radiation source emitting an electromagnetic wave. Wave portions of a higher wave type (TE.sub.01) are coupled out at a plurality of locations on the inner circumferential surface of the horn and the wave portions are combined in an annular rectangular wave guide extending around the outer circumference of the horn radiator.
Such grooved horn radiators are used in ground station antennae in which equivalent field patterns of the ground waves in two main coordinate planes are required on the one hand and receiving devices for at least one higher wave type with a marked zero position in the center of the ground wave field patterns are necessary on the other hand for exact alignment of an antenna with a satellite.
A receiving antenna is disclosed in German Auslegeschrift No. 14 91 921 for the automatic tracking of a moving radiation source and the antenna comprises a smooth-walled horn radiator. An annular rectangular wave guide is arranged on this horn radiator in the coupling plane of the TE.sub.01 wave type, and the wave energy of the TE.sub.01 wave is transmitted from the horn radiator via four windows into the annular rectangular wave guide and a further rectangular wave guide leads away from the first mentioned wave guide. The additional wave guide contains a ground wave whose energy is proportional to the coupled out TE.sub.01 wave type from the horn radiator. This type of coupling out of the TE.sub.01 wave, however, is suitable only for thin-walled horn radiators with a smooth inner wall or surface.